GLIRES OF THE SANTA CRUZ BEDS. 441 



of wear ; the specimen consists of the greater part of a skeleton, unfortu- 

 nately in a very much damaged condition. The lower incisors, which 

 protrude but little above the alveoli, are narrow and have slightly convex 

 faces, which are faintly grooved. In its unworn state, p^ appears to have 

 two valleys, one of which is the true valley and the other is a deep notch, 

 demarcating the internal pillar, which is very prominent ; all the lower 

 molars likewise have well marked internal pillars, produced by the pro- 

 jection of the posterior lamina. Of the skull, only the tympanic bullae 

 and the mandible are preserved ; the bullae are relatively very large, and 

 the horizontal ramus is long, low and thick, and the much damaged angle 

 ends in a very long process, which extends behind the bulla. Most of the 

 limb-bones have lost their epiphyses, so that it is not practicable to give 

 their dimensions, save in a few instances. A description of these bones, 

 parts of the scapula, ulna, metacarpal III, femur, tibia, calcaneum and 

 astragalus has been given in the account of the genus. 



In the following table the measurements of the upper teeth are from the 

 type in the Ameghino collection, the others are from No. 15,063. 



MEASUREMENTS. 



Upper dentition, length pA-m-S. 012 M^, width 003 



Ml, length (i. e., antero-posterior diam- Mandible, depth at p^ 008 



eter) 002 " " " notch in front of p^ . .005 



Ml, width (i. e., transverse diameter) . .0035 Mandible, thickness at p ? 0065 



M&, length 004 Scapula, height (approximate) 032 



- " width 0035 " width of neck 004 



Ulna, width at sigmoid notch 004 



Lower dentition, length 025 Metacarpal III, proximal width 0025 



P*~ m * OI 3 Tibia,length 044 



Lower incisor, width 002 ^^ width Qo6 



thickness 2 thickness 005 



M T> fcng* 3 Astragalus, length 008 



Wldth 3 width of trochlea 005 



M^, length 003 



PERIMYS PERPINGUIS Ameghino. 



(Plate LXVIII, Figs, n, 12.) 



Perimys perpinguis Amegh.; Rev. Argent, de Hist. Nat; T. I, 1891, p. 



144. 



A species of medium size, larger than any of the preceding ones, 

 but much smaller than others ; the type is a fragment of mandible with 



